1. Field of the Invention
The present invention relates to a camera, and more specifically, to a camera auto-focus mechanism.
2. Description of the Prior Art
Most automatic cameras include a device for automatically focusing a subject to be photographed. An auto-focus device does not require the user to manually bring the subject into focus, thereby reducing focusing errors and making modern automatic cameras easy to use.
A typical auto-focus device is controlled by a microcontroller to control the relative position of a pair of lenses. The microcontroller also coordinates other devices to perform an active range finding function (e.g. infrared) or a passive range finding function. Once the range of the subject from the camera is determined the microcontroller controls the auto-focus device to position the lenses to correctly focus the subject.
Cost effective automatic cameras usually employ a two-position lens system where the lens system is set to either a far-focus or a near-focus position. A simplified range finding system provides ranging information to a microcontroller that controls the two positional lens system. Focus is then automatically established based on the subject being at infinity or at a normal subject distance of about 8-12 feet (2.4-3.6 meters).
Conventional auto-focus mechanisms, which are currently used in cameras, do not use space economically and have overly complicated linkage mechanisms and other unnecessary components. An improved auto-focusing mechanism is required to reduce size, weight, and costs of modern automatic cameras.
It is therefore a primary objective of the claimed invention to provide a space-saving and cost effective two-position camera auto-focus mechanism to solve the above problems.
Briefly summarized, an embodiment of the claimed invention includes a frame having a first hollow cylinder having a circular opening, a first lens fixed to the frame and axially aligned with the circular opening, an insulated conductive metal coil wound around the first cylinder, a second hollow cylinder including metal material fitting over the first cylinder and capable of moving relative to the first cylinder along a central axis, a second lens fixed inside the second cylinder and axially aligned with the circular opening, and an elastic member, such as a spring axially aligned with the circular opening, joining the second cylinder and the first cylinder. When electrical current is not applied to the coil, the second cylinder is held in a first position by the elastic member such that the first and second lenses form a first focal length. And, when electrical current is applied to the coil, the second cylinder is held in a second position against a force of the elastic member such that the first and second lenses form a second focal length.
According to another embodiment of the claimed invention, the positions of the coil and the metal material are exchanged.
It is an advantage of the claimed invention that the coil and the metal in the second cylinder form a solenoid-type actuator thereby providing actuation and structure with the same components.
It is a further advantage of the claimed invention that the coaxial arrangement of the cylinders, lenses, metal material, and spring provides a space-economic arrangement.
It is a further advantage of the claimed invention that the energized coil draws the second cylinder to the second position against the elastic member, and the elastic member acts to return the second cylinder to the first position when the coil is not conducting current so that the auto-focus mechanism can be easily used in any orientation.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.